The EN 300 421 standard of the ETSI (European Telecommunications Standards Institute) relates to DVB services over transparent satellite communication systems. The purpose of this standard is the provisioning of direct-to-user services known as DVB-S (digital video broadcasting via satellite), through an integrated receiver/decoder device that is located in his home. Its flexibility in multiplexing permits the use of a transmission capacity encompassing a variety of television (TV) service configurations, including sound and data services. All the components of said services are time division multiplexed (TDM) on a single carrier. The most detailed description of this standard can be found in the ETSI publication EN 300 421 V1.1.2 (1997-98) entitled: “Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for 11/12 GHz satellite services”, the content of which is included in this patent application by reference.
Moreover, the ETSI standard known as DVB-RCS001 makes reference to interaction channels on a transparent satellite distribution system. The purpose of this standard is to provide basic specifications for the provision of interaction channels for interactive networks based on geostationary satellites (GEO) that incorporate fixed return channel satellite terminals (RCST). The service is also known as DVB-RCS (digital video broadcasting—return channel satellite). This standard facilitates the use of RCSTs for domestic installations both individual and collective types. Likewise, it supports the connection of said terminals with data networks at home, and can be applied to all the frequency bands allocated to GEO satellite services. The most detailed description of this standard can be found in the ETSI publication TM2267r3DVB-RCS001rev12 (Feb. 11, 2000) entitled: “Digital Video Broadcasting (DVB); Interaction Channel for Satellite Distribution Systems”, the content of which is included in this patent application by reference.
These two standards are of the mono-spot type; that is, the satellite defines a single zone as coverage area. The mono-spot systems therefore present the drawback that, by having limited coverage areas, they are not suitable for more extensive areas on a worldwide scale. The services related with each of said standards are presently employed in a mutually independent form.
The steadily growing user demand for interactive services makes it necessary for the satellite communication systems to support broadcasting with return channel to the end users when the latter may be scattered over entirely different and dislike regions of the world, and thereby facilitate better access and faster interconnection between them. This, in turn, makes it necessary the provision of systems capable of broadcasting on networks that support multimedia having multispot communication characteristic.
The service that DVB-S provides, although offering the possibility of direct communication to the user's home, has the drawback of not having foreseen the possibility of including a return channel in order that the user may communicate with the multimedia service provider. On the other hand, the service furnished through DVB-RCS, whilst providing said return channel, does not include the possibility of direct communication with the user's home for broadcast applications.
In the light of the foregoing, it has become necessary to facilitate an integrated multispot satellite communication system on a multimedia broadcasting network capable of supporting digital video broadcasting (DVB) applications in order to facilitate multimedia services directly to the user's home and permitting at the same time that said user can establish communication with the multimedia service provider over a return channel.
One solution to this problem, proposed by this same applicant, has been to offer the users a multimedia broadcasting service such that the user can communicate with the multimedia service provider via a return channel to the satellite, all of this in a substantially economical manner.
Said solution proposed the combined use of the standardised DVB-S and DVB-RCS services, thereby obtaining a single, regenerative and multispot, satellite system permitting the use of standard stations both on the transmission and on the reception side. With this solution, both the end user and the multimedia service provider employ a return channel according to the DVB-RCS standard via an uplink channel to the satellite.
On board the satellite the regenerative payload performs the multiplexing of the information coming from diverse sources into a data stream suitable for being received by a user who has available any standard integrated receiver/decoder equipment.
Moreover, according to the ETSI standard DVB-RCS001 (draft EN 301 790 V1.1.1.) relative to the interaction channels in satellite systems, the synchronisation of the bursts transmitted by the return channel satellite terminal (RCST) is carried out by receiving information on a network clock reference (NCR) inside the standard packets termed MPEG2-TS (Motion Picture Expert Group 2-Transport Stream), sent by a network control centre in DVB-S format. The RCST reconstructs the original 27 MHz reference of the network control centre, permitting it to transmit the return information in burst mode in an allocated time slot.
As has already been mentioned, the mutually independent and transparent use of the two broadcasting and interaction services performed in a conventional manner makes it unnecessary to have synchronisation of the bursts in transmission of the programs offered to the users, thus the RCST could strictly employ the DVB-RCS standard.
However, on combining the two services, DVB-S and DVB-RCS, that is when using an integrated broadcast and interaction system as has been mentioned above, it is assumed that the RCSTs used by the broadcast provider shall be the same as those used by the users. For this purpose it is necessary to define a burst synchronisation method that is common both for the interactive services and for broadcasting, and consequently permits the use of the same type of RCST on the service provider side and on the user side.